This invention pertains to a liner system for a double wall tank. More particularly the invention is directed to a liner system which extends between a spaced inner tank bottom and outer tank bottom of a tank and aids in providing leaking fluid egress from between the tank bottoms while supporting the inner tank bottom.
The above related application and its parent application now U.S. Pat. No. 4,840,283 is directed to a double containment tank particularly a liquid/solids clarifier or thickener tank where a normally conically sloped steel or concrete or plastic liner type outer bottom tank is provided with a sloped pervious layer of oiled sand confined in part by a series of support bars. An inner tank bottom in the form of welded steel sheets or other tank material is positioned on the oiled sand and bars. Any solids/liquid fluid leakage from the inner tank, either through the inner tank bottom or through the tank inner side walls, is transported through the sand to a desired location normally in or adjacent to the space between the inner and outer tank bottoms or between the walls of a double walled solids discharge cone in the inner bottom. A leak detector probe accesses leakage at that location, alerting operators to the presence of any leak occurring in the inner tank.
It has been found to be difficult, time consuming, labor intensive and expensive to form an inclined or inverse conical sand layer over a large surface area of an outer bottom. These areas may be as much as 6648 square meters. Further, the cost and weight of the support bars results in relatively high construction costs. Additionally, a tank supplier must rely on subcontractors to expeditiously supply sand and oil mixing facilities during installation. The oiled sand also acts to contaminate any leakage which might otherwise be recovered prior to repairing an identified leak. Further while oiled sand is fairly incompressible it can be caused to move by the loading within the tank not only packing the sand but actually causing it to move as earth moves under pressure. The spacing between the inner and outer bottoms can thus decrease, overall or locally, placing load strains on plate joints such as at the welds, to the detriment of the overall integrity of the inner tank. Thus a need has existed for a better dual containment tank support construction.